Cylindrical lithium-ion cell

ABSTRACT

A cylindrical lithium ion battery in which an electrode group formed by winding a positive electrode and a negative electrode is housed in a battery case is disclosed. A sealing plate seals an opening of the battery case. An insulating plate having a plurality of openings is provided on a side of the electrode group closer to the sealing plate. The plurality of openings include a first hole with a largest opening area, and a plurality of second holes with opening areas smaller than the opening area of the first hole. An opening ratio of the first hole is 12% or more and 40% or less; a sum of opening ratios of the second holes is 0.3% or more and 10% or less; and a total opening ratio of all the openings is 20% or more and 50% or less.

RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 15/268,093, filed on Sep. 16, 2016, which is adivisional patent application of U.S. patent application Ser. No.14/369,140, filed on Jun. 26, 2014, now U.S. Pat. No. 9,472,795, issuedon Oct. 18, 2016, which is a National Phase of International PatentApplication No. PCT/JP2012/008463, filed on Dec. 28, 2012, which in turnclaims the benefit of Japanese Patent Application No. 2011-288466, filedon Dec. 28, 2011, the disclosure of which applications are incorporatedby reference herein.

TECHNICAL FIELD

The present disclosure relates to lithium ion batteries, andspecifically relates to improvement of upper insulating plates ofcylindrical batteries.

BACKGROUND ART

In general, cylindrical batteries are configured such that apower-generating element is accommodated in a bottomed metal batterycase, with its opening sealed with a metal sealing plate. In secondarybatteries, such as lithium ion secondary batteries, the power-generatingelement is comprised of an electrode group and an electrolyte. Theelectrode group is formed by spirally winding a positive electrode and anegative electrode, with a separator sandwiched therebetween. Theseparator insulates the positive electrode and the negative electrodefrom each other, and has a function of holding the electrolyte.

The sealing plate has a valve mechanism configured to ensure batterysafety. In the event where an abnormal condition occurs in the battery,and the pressure in the battery case increases to a predetermined value,the valve mechanism is opened to release the gas in the battery case,thereby preventing an accident, such as a crack in the battery case.

Recently, however, with increasing functionality of electric devices,further increases in battery capacities are promoted, which as a resultfurther increases a pressure in the battery case in the event where anabnormal condition occurs in the battery. In particular, the upperinsulating plate on the edge of the electrode group may not be able towithstand the pressure and be deformed, and the electrode group may moveupward and close an exhaust hole. To avoid this, various techniques forensuring battery safety have been suggested.

For example, Patent Document 1 discloses a technique in which a diameterof the upper insulating plate is equal to or larger than an insidediameter of a groove formed in the battery case to reduce displacementof the electrode group.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No.2002-100343

SUMMARY OF THE INVENTION Technical Problem

However, in conventional cylindrical batteries, sometimes there werecases in which when the pressure in the battery case abnormallyincreased, a central portion of the upper insulating plate was curved,and the electrode group moved upward, for example, and closed a valvehole that was formed when a rupture valve body in a sealing plate wasruptured. In such a case, the gas in the battery case might not beimmediately released.

The present disclosure is thus intended to provide cylindrical batterieswith improved safety, in which a valve hole in a valve plate included ina sealing plate is prevented from being closed by deformation of aninsulating plate in the event where a pressure in a battery case isincreased.

Solution to the Problem

To achieve the above objective, a cylindrical lithium ion batteryaccording to the present disclosure is a cylindrical lithium ion batteryin which an electrode group formed by winding a positive electrode and anegative electrode, with a separator interposed therebetween, is housedin a battery case, wherein a sealing plate having a gas exhaust valveseals an opening of the battery case, with a gasket interposedtherebetween, an insulating plate having a plurality of openings isprovided on a side of the electrode group closer to the sealing plate,the plurality of openings include a first hole with a largest openingarea, and a plurality of second holes each with an opening area smallerthan the opening area of the first hole, and in the insulating plate, anopening ratio of the first hole is 12% or more and 40% or less, a sum ofopening ratios of the second holes is 0.3% or more and 10% or less, anda total opening ratio of all the openings is 20% or more and 50% orless.

The plurality of second holes may have the same opening areas, or mayhave opening areas different from each other. Further, the shapes of thefirst hole and the second holes are not specified.

The opening ratio of the first hole with a largest opening area ispreferably 12% or more for ensuring penetration of the electrolyte intoelectrode group, and preferably 40% or less for ensuring insulatingproperties. Further, the sum of the opening ratios of the second holeseach with an opening area smaller than the opening area of the firsthole is preferably 0.3% or more for ensuring processability, andpreferably 10% or less for ensuring insulating properties. Further, thetotal opening ratio of all the openings is preferably 20% forimmediately exhausting gas generated from the electrode group in theevent of an abnormal condition to the outside, and preferably 50% orless for reducing the displacement of the electrode group.

Advantages of the Invention

According to the present disclosure, gas generated from the electrodegroup can be immediately released in the event where the pressure in thebattery case is increased, and deformation of the insulating plate canbe prevented even in the case where the pressure in the battery case isincreased. As a result, the electrode group does not move upward, andthe valve hole is not closed. Thus, the battery safety can be improvedaccording to the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view, showing a schematic configuration of acylindrical battery according to an embodiment of the presentdisclosure.

FIG. 2 is a schematic view of an upper insulating plate according to anembodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS First Embodiment

An embodiment of the present disclosure will be described in detailbelow with reference to the drawings.

FIG. 1 is a cross-sectional view, showing a schematic configuration of acylindrical battery according to an embodiment of the presentdisclosure. The battery 10 shown in FIG. 1 is a cylindrical lithium ionsecondary battery, and includes an electrode group 20 that is formed byspirally winding a positive electrode 2, a negative electrode 3, and aseparator 4 interposed between the positive electrode 2 and the negativeelectrode 3. The electrode group 20 is accommodated in a bottomedcylindrical metal battery case 1 together with a nonaqueous electrolyte(not shown). An opening of the battery case 1 is sealed with a sealingplate 5. Thus, the electrode group 20 and the nonaqueous electrolyte aresealed inside the battery case 1.

The sealing plate 5 is comprised of a hat-like terminal plate 11, apositive temperature coefficient (PTC) thermistor plate 12 in an annularshape, a circular upper valve plate 13, a circular lower valve plate 15,and a substrate 16, which all are made of conductive materials, and anannular inner gasket 14 made of an insulating material. The inner gasket14 is provided between a periphery of the upper valve plate 13 and aperiphery of the lower valve plate 15 to avoid contact between theperiphery of the upper valve plate 13 and the periphery of the lowervalve plate 15. Further, the inner gasket 14 intervenes between acylindrical portion 16 b of the substrate 16, described later, and acircumference of the terminal plate 11 to avoid contact therebetween.

An outer gasket 17 made of an insulating material is provided between acircumference of the sealing plate 5 and the opening of the battery case1. The outer gasket 17 seals between the sealing plate 5 and the batterycase 1, and provides insulation between the sealing plate 5 and thebattery case 1.

The terminal plate 11 and the PTC thermistor plate 12 are in contactwith each other at their peripheries. The PTC thermistor plate 12 andthe upper valve plate 13 are in contact with each other at theirperipheries. The upper valve plate 13 and the lower valve plate 15 arewelded to each other at their central portions. The lower valve plate 15and the substrate 16 are in contact with each other at theirperipheries. Accordingly, the terminal plate 11 and the substrate 16 areconductively connected with each other.

The substrate 16 of the sealing plate 5 is conductive with the positiveelectrode 2 via a positive electrode lead 6. Thus, the terminal plate 11of the sealing plate 5 functions as an external terminal on the positiveelectrode side of the battery 10. On the other hand, the battery case 1is conductive with the negative electrode 3 l via a negative electrodelead 7, and functions as an external terminal on the negative electrodeside of the battery 10.

The substrate 16 includes a body 16 a in a shallow round plate-likeshape, and a cylindrical portion 16 b which stands upright from thecircumference of the body 16 a. The lower valve plate 15 is placed onthe periphery of the body 16 a of the substrate 16. The inner gasket 14is further placed on that periphery. The upper valve plate 13, the PTCthermistor plate 12, and the terminal plate 11 are sequentially placedon the inner gasket 14. An outer edge portion of the inner gasket 14protrudes from an end of the cylindrical portion 16 b of the substrate16. In this state, the upper end of the cylindrical portion 16 b of thesubstrate 16 is bent inward and crimped, and as a result, the terminalplate 11, the PTC thermistor plate 12, the upper valve plate 13, theinner gasket 14, and the lower valve plate 15 are held by the substrate16. Here, the circumferences of the terminal plate 11, the PTCthermistor plate 12, and the upper valve plate 13 are separated from,and is not in contact with the cylindrical portion 16 b of the substrate16, due to the inner gasket 14.

The terminal plate 11 of the sealing plate 5 has a plurality of externalgas vents 22. The substrate 16, too, has a plurality of internal gasvents 21.

The upper valve plate 13 has a circular inside portion 13 b surroundedby an annular groove 13 a, in a central portion. The inside portion 13 bof the upper valve plate 13 is supported by an outside portion 13 csurrounding the inside portion 13 b. When the inside portion 13 b isruptured, a valve hole is formed there.

On the other hand, the lower valve plate 15 has a circular insideportion 15 b surrounded by an annular groove 15 a, in a central portion.The inside portion 15 b of the lower valve plate 15 is supported by anoutside portion 15 c surrounding the inside portion 15 b. When theinside portion 15 b is ruptured, a valve hole is formed there.

The diameter of the inside portion 15 b of the lower valve plate 15 isslightly smaller than the diameter of the inside portion 13 b of theupper valve plate 13. The entire inside portion 15 b of the lower valveplate 15 overlaps the inside portion 13 b of the upper valve plate 13.

The inside diameter of the central hole of the annular PTC thermistorplate 12 is slightly larger than the diameter of the rupturable portion13 b of the upper valve plate 13. The entire rupturable portion 13 b ofthe upper valve plate 13 overlaps a projection shape of the central holeof the PTC thermistor plate 12. The inside diameter of the central holeof the inner gasket 14 is larger than the inside diameter of the centralhole of the PTC thermistor plate 12. The entire projection shape of thecentral hole of the PTC thermistor plate 12 overlaps the projectionshape of the central hole of the inner gasket 14.

The substrate 16 has a plurality of internal gas vents 21, and is weldedto the positive electrode lead at the body 16 a. In the battery case 1,an upper insulating plate 8 and a lower insulating plate 9 are providedabove and under the electrode group 20.

As shown in FIG. 2, the upper insulating plate 8 has a plurality of gasvents, i.e., a hole 8 a having a largest opening area and the otherholes 8 b. The opening ratio of the hole 8 a having the largest openingarea is 12% or more and 40% or less, and a sum of the opening ratios ofthe other holes 8 b is 0.3% or more and 10% or less. A total openingratio is 20% or more and 50% or less.

In the above configurations, the rupturable portions 13 b and 15 b ofthe upper valve plate 13 and the lower valve plate 15 are broken andvalve holes (not shown) are formed in the upper valve plate 13 and thelower valve plate 15, in the event where some accident occurred and thepressure in the battery case 1 abnormally increased. As a result, gas inthe battery case 1 is released to the outside through the gas vents 8 aand 8 b of the upper insulating plate 13, the internal gas vents 21 ofthe substrate 16, the valve holes of the upper valve plate 13 and thelower valve plate 15, and the external gas vents 22 of the terminalplate 11.

Further, when an excessively large current flows through the PTCthermistor plate 12, the temperature of the PTC thermistor plate 12increases, and the PTC thermistor plate 12 cuts off the current.

Sometimes there are cases in which the pressure in the battery case 1abnormally increases. In such a situation, as well, it is possible toprevent the deformation of the upper insulating plate 8 caused by anincrease of pressure in the battery case 1, and possible to prevent thevalve holes of the upper valve plate 13 and the lower valve plate 15from being completely closed by the electrode group 20 which has movedup, because the opening ratio of the hole 8 a of the upper insulatingplate 8, which has the largest opening area, is 12% or more and 40% orless, and the sum of the opening ratios of the other holes 8 b is 0.3%or more and 10% or less, and the total opening ratio is 20% or more and50% or less. As a result, it is possible to ensure a path for releasinggas from the battery case 1. The battery safety can therefore beimproved.

The first embodiment of the present disclosure has been described withreference to FIG. 1 and FIG. 2, but the present disclosure is notlimited to the first embodiment.

EXAMPLES

Next, examples of the present disclosure according to the firstembodiment will be described.

First Example

Specimens comprised of lithium ion secondary batteries were fabricatedin the following manner.

(Fabrication of Positive Electrode)

A lithium nickel-containing composite oxide(LiNi_(0.85)Co_(0.1)Al_(0.05)) with an average particle diameter of 10μm was used as a positive electrode active material. A positiveelectrode mixture paste was prepared by mixing 8 percent by weight ofpolyvinylidene fluoride (PVDF) as a binder, 3 percent by weight ofacetylene black as a conductive material, and an adequate amount ofN-Methyl-2-Pyrrolidone (NMP), in 100 percent by weight of the positiveelectrode active material.

The positive electrode mixture paste was applied to both surfaces of apositive electrode current collector 2 a made of aluminum foil, exceptan area where a positive electrode lead 6 was to be connected, and wasdried to obtain a positive electrode mixture layer 2 b. A precursor of apositive electrode was fabricated in this manner, and the precursor wasrolled to obtain a positive electrode. At this moment, the precursor ofthe positive electrode was rolled such that the thickness of thepositive electrode mixture layer 2 b per surface of the positiveelectrode current collector 2 a would be 70 μm.

The aluminum foil used as the positive electrode current collector 2 ahad a length of 600 mm, a width of 54 mm, and a thickness of 20 μm.Further, the area where the positive electrode lead 6 was to beconnected was formed at a start end of the winding of the positiveelectrode, as described later.

Fabrication of Negative Electrode

Artificial graphite with an average particle diameter of 20 μm was usedas a negative electrode active material. A negative electrode mixturepaste was prepared by mixing 1 percent by weight of styrene-butadienerubber as a binder, 1 percent by weight of carboxymethylcellulose as athickener, and an adequate amount of water, in 100 percent by weight ofthe negative electrode active material.

The negative electrode mixture paste was applied to both surfaces of anegative electrode current collector 3 a made of copper foil, except anarea where a negative electrode lead 7 was to be connected, and wasdried to obtain a negative electrode mixture layer 3 b. A precursor of anegative electrode was fabricated in this manner, and the precursor wasrolled to obtain a negative electrode. At this moment, the precursor ofthe negative electrode was rolled such that the thickness of thenegative electrode mixture layer 3 b per surface of the negativeelectrode current collector 3 a would be 65 μm.

The copper foil used as the negative electrode current collector 3 a hada length of 630 mm, a width of 56 mm, and a thickness of 10 μm. Further,the area where the negative electrode lead 7 was to be connected wasformed at a finish end of the winding of the negative electrode. Thenegative electrode lead 7 was connected to the connection area byultrasonic bonding.

Fabrication of Sealing Plate

The sealing plate 5 shown in FIG. 1 was fabricated. The upper valveplate 13 and the lower valve plate 15 were made of aluminum. Theterminal plate 11 was made of iron. The substrate 16 was made ofaluminum. The inner gasket 14 was made of polypropylene. Two internalgas vents 21 were formed in the bottom of the substrate 16.

Assembly of Battery

The positive electrode and the negative electrode fabricated in theabove manner were layered, with a separator 4 interposed therebetween,and a layered structure was formed. A porous film made of polyethyleneand having a thickness of 20 μm was used as the separator 4. In theobtained layered structure, a positive electrode lead 6 was connected tothe start end of the winding of the positive electrode, and a negativeelectrode lead 7 is connected to the finish end of the winding of thenegative electrode. In this state, the layered structure was spirallywound to form an electrode group 20.

The thus obtained electrode group 20 was housed in the battery case 1made of iron. At this time, the positive electrode lead 6 was welded, bylaser welding, to the substrate 16 of the sealing plate 5 to thecircumference of which an outer gasket 17 made of polypropylene had beenattached, and the negative electrode lead 7 was welded to the bottom ofthe battery case 1 by resistance welding. The battery case 1 having adiameter (outside diameter) of 18 mm, a height of 65 mm, and a wallthickness of 0.15 mm was used. The thickness of the battery case 1 isclose to the thicknesses of the battery cases of commonly-marketedcylindrical lithium ion secondary batteries. An upper insulating plate 8made of glass phenolic resin and a lower insulating plate 9 made ofpolypropylene were provided above and under the electrode group 20. Theupper insulating plate 8 in which: the opening ratio of a hole 8 a witha largest opening area was 30%; a sum of the opening ratios of the otherholes 8 b was 5%; and a total opening ratio was 35%, was used.

After that, a nonaqueous electrolyte was injected into the battery case1. The nonaqueous electrolyte was prepared by dissolving lithiumhexafluorophosphate (LiPF₆) at a concentration of 1.0 mol/L into a mixedsolution of ethylene carbonate and ethyl methyl carbonate mixed in aone-to-one volume ratio.

Subsequently, the battery case 1 was provided with a projected portionla (see FIG. 1) projecting inward at a location 5 mm from the open endof the battery case 1 and circling around the battery case 1 in acircumferential direction to hold the electrode group 20 by the batterycase 1.

Next, the sealing plate 5 was positioned in the opening of the batterycase 1 by placing it on the projected portion 1 a. Thereafter, theopening of the battery case 1 was bent inward and crimped to seal thebattery case 1.

In this manner, ten specimens of cylindrical lithium ion secondarybatteries each having a diameter of 18 mm and a height of 65 mm werefabricated. The capacity of the lithium ion secondary battery wasdesigned to be 3400 mAh.

The ten specimens were subjected to the following test. First, thespecimens were charged in an environment of a temperature of 25° C. at acurrent of 1500 mA until the battery voltage was 4.25 V. The chargedspecimens were placed on a hot plate and heated at a temperature of from25° C. to 200° C. such that the temperature was increased by 1° C. persecond, and the number of specimens having a crack in the battery case 1was counted. The results are shown in Table 1 below.

Second Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 12%; a sum of the opening ratios of theother holes 8 b was 9%; and a total opening ratio was 21%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Third Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 40%; a sum of the opening ratios of theother holes 8 b was 5%; and a total opening ratio was 45%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Fourth Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 30%; a sum of the opening ratios of theother holes 8 b was 0.3%; and a total opening ratio was 30.3%. Thespecimens were subjected to the same test conducted in the firstexample. The results are shown in Table 1 below.

Fifth Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 30%; a sum of the opening ratios of theother holes 8 b was 10%; and a total opening ratio was 40%. Thespecimens were subjected to the same test conducted in the firstexample. The results are shown in Table 1 below.

Sixth Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 17%; a sum of the opening ratios of theother holes 8 b was 3%; and a total opening ratio was 20%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Seventh Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 40%; a sum of the opening ratios of theother holes 8 b was 10%; and a total opening ratio was 50%. Thespecimens were subjected to the same test conducted in the firstexample. The results are shown in Table 1 below.

Eighth Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 21%; a sum of the opening ratios of theother holes 8 b was 9%; and a total opening ratio was 30%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Ninth Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 29%; a sum of the opening ratios of theother holes 8 b was 1%; and a total opening ratio was 30%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Tenth Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 33%; a sum of the opening ratios of theother holes 8 b was 9.5%; and a total opening ratio was 42.5%. Thespecimens were subjected to the same test conducted in the firstexample. The results are shown in Table 1 below.

First Comparative Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 15%; a sum of the opening ratios of theother holes 8 b was 3%; and a total opening ratio was 18%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Second Comparative Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 13%; a sum of the opening ratios of theother holes 8 b was 2%; and a total opening ratio was 15%. The specimenswere subjected to the same test conducted in the first example. Theresults are shown in Table 1 below.

Third Comparative Example

Ten specimens of lithium ion secondary batteries were fabricated in asimilar manner as in the first example, except that a following upperinsulating plate 8 was used in which: the opening ratio of the hole 8 awith a largest opening area was 12%; a sum of the opening ratios of theother holes 8 b was 0.3%; and a total opening ratio was 12.3%. Thespecimens were subjected to the same test conducted in the firstexample. The results are shown in Table 1 below.

TABLE 1 OPENING SUM OF RATIO OPENING TOTAL NUMBER OF OF RATIOS OFOPENING SPECIMENS HOLE 8a HOLES 8b RATIO WITH CRACKS EXAMPLE 1 30 5 35 0EXAMPLE 2 12 9 21 0 EXAMPLE 3 40 5 45 0 EXAMPLE 4 30 0.3 30.3 0 EXAMPLE5 30 10 40 0 EXAMPLE 6 17 3 20 0 EXAMPLE 7 40 10 50 0 EXAMPLE 8 21 9 300 EXAMPLE 9 29 1 30 0 EXAMPLE 10 33 9.5 42.5 0 COMPARATIVE EXAMPLE 1 153 18 2 COMPARATIVE EXAMPLE 2 13 2 15 4 COMPARATIVE EXAMPLE 3 12 0.3 12.36

As shown in Table 1, cracks did not occur in the specimens of the firstto tenth examples. This may be because the gas generated from theelectrode group was immediately released since the total opening ratiois 20% or more in each of the first to tenth examples, and because thevalve hole was not closed since the upper insulating plate was preventedfrom being deformed and upward movement of the electrode group wasprevented. Here, the movement of the electrode group cannot be preventedwhen the total opening ratio exceeds 50%.

On the other hands, cracks occurred in some of the specimens of thefirst to third comparative examples. This may be because the totalopening ratio is low in each of the first to third comparative examples,and therefore, the gas generated from the electrode group could not beimmediately released when the pressure in the battery case wasincreased, and as a result, the upper insulating plate was deformed withan increase of the pressure in the battery case, causing and theelectrode group to move upward and close the valve hole.

The opening ratio of the first hole 8 a with a largest opening area ispreferably 12% or more for ensuring penetration of the electrolyte intothe electrode group, and preferably 40% or less for ensuring insulatingproperties. Further, the sum of the opening ratios of the second holes 8b each having an opening area smaller than the opening area of the firsthole 8 a is preferably 0.3% or more in view of processability, andpreferably 10% or less for ensuring insulating properties.

In lithium ion batteries with an increased capacity, the pressure in thebattery case increases more rapidly. Thus, the total opening ratio ispreferably 30% or more. Further, total opening ratio is preferably 40%or less in view of reducing the displacement of the electrode group.

As described above, by using the upper insulating plate in which theopening ratio of the hole 8 a with a largest opening area is 12% or moreand 40% or less; the sum of the opening ratios of the other holes 8 b is0.3% or more and 10% or less; and the total opening ratio is 20% or moreand 50% or less, it is possible to prevent an increase of the pressurein the battery case, while ensuring penetration of the electrolyte andinsulating properties. The safety of the cylindrical battery istherefore improved.

INDUSTRIAL APPLICABILITY

The cylindrical lithium ion battery of the present disclosure is usefulas a power source of portable electric devices such as personalcomputers, mobile phones and mobile devices, or as an auxiliary powersource of electric motors of hybrid cars, electric cars, etc.

DESCRIPTION OF REFERENCE CHARACTERS

1 battery case

2 positive electrode

2 a positive electrode current collector

2 b positive electrode mixture layer

3 negative electrode

3 a negative electrode current collector

3 b negative electrode mixture layer

4 separator

5 sealing plate

6 positive electrode lead

7 negative electrode lead

8 upper insulating plate

9 lower insulating plate

10 battery

11 terminal plate

12 PTC thermistor plate

13 upper valve plate

14 inner gasket

15 lower valve plate

16 substrate

17 outer gasket

20 electrode group

21 internal gas vent

22 external gas vent

The invention claimed is:
 1. A cylindrical lithium ion battery in whichan electrode group formed by winding a positive electrode and a negativeelectrode, with a separator interposed therebetween, is housed in abattery case, wherein: a sealing plate having a gas exhaust valve sealsan opening of the battery case, with a gasket interposed therebetween,an insulating plate having a plurality of openings is provided on a sideof the electrode group closer to the sealing plate, the plurality ofopenings include a first hole with a largest opening area, and aplurality of second holes each with an opening area smaller than theopening area of the first hole, and the plurality of second holes haveopening areas different from each other.
 2. The cylindrical lithium ionbattery of claim 1, wherein: a shape of the first hole and a shape ofeach of the second holes are different.
 3. The cylindrical lithium ionbattery of claim 1, wherein: a positive electrode lead is connected tothe positive electrode, and the positive electrode lead is led from thefirst hole.
 4. The cylindrical lithium ion battery of claim 1, wherein:an opening ratio of the first hole is 12% or more and 40% or less. 5.The cylindrical lithium ion battery of claim 1, wherein: a sum ofopening ratios of the second holes is 0.3% or more and 10% or less.
 6. Acylindrical lithium ion battery in which an electrode group formed bywinding a positive electrode and a negative electrode, with a separatorinterposed therebetween, is housed in a battery case, wherein: a sealingplate having a gas exhaust valve seals an opening of the battery case,with a gasket interposed therebetween, an insulating plate having aplurality of openings is provided on a side of the electrode groupcloser to the sealing plate, the plurality of openings include a firsthole with a largest opening area, and a plurality of second holes eachwith an opening area smaller than the opening area of the first hole,and a shape of the first hole and a shape of each of the second holesare different.
 7. The cylindrical lithium ion battery of claim 6,wherein each of the plurality of second holes has a same opening area.8. The cylindrical lithium ion battery of claim 6, wherein: a positiveelectrode lead is connected to the positive electrode, and the positiveelectrode lead is led from the first hole.
 9. The cylindrical lithiumion battery of claim 6, wherein an opening ratio of the first hole is12% or more and 40% or less.
 10. The cylindrical lithium ion battery ofclaim 6, wherein a sum of opening ratios of the second holes is 0.3% ormore and 10% or less.
 11. A cylindrical lithium ion battery in which anelectrode group formed by winding a positive electrode and a negativeelectrode, with a separator interposed therebetween, is housed in abattery case, wherein: a sealing plate having a gas exhaust valve sealsan opening of the battery case, with a gasket interposed therebetween,an insulating plate having a plurality of openings is provided on a sideof the electrode group closer to the sealing plate, the plurality ofopenings include a first hole with a largest opening area, and aplurality of second holes each with an opening area smaller than theopening area of the first hole, and an opening ratio of the first holeis 12% or more and 40% or less.
 12. The cylindrical lithium ion batteryof claim 11, wherein: a positive electrode lead is connected to thepositive electrode, and the positive electrode lead is led from thefirst hole.
 13. The cylindrical lithium ion battery of claim 11, whereina sum of opening ratios of the second holes is 0.3% or more and 10% orless.
 14. The cylindrical lithium ion battery of claim 11, wherein atotal opening ratio of all the openings is 20% or more and 50% or less.